Photofabrication, which is now the most widely used technique for precision microprocessing, is a generic term describing the technology used for manufacturing precision components such as semiconductor packages by applying a photosensitive resin composition to the surface of a processing target to form a coating, patterning this coating using photolithography techniques, and then conducting chemical etching or electrolytic etching, and/or electroforming based mainly around electroplating, using the patterned coating as a mask.
Recently, reductions in the size of electronic equipment have lead to further developments in higher density packaging of semiconductor packages, including multipin thin-film packaging, reductions in package size, two dimensional packaging techniques using flip-chip systems, and other improvements in packaging density based on three dimensional packaging techniques. In these types of high density packaging techniques, connection terminals, including protruding electrodes (mounting terminals) such as bumps which protrude above the package, and metal posts that connect rewiring extending from peripheral terminals on the wafer with the mounting terminals, must be positioned on the surface of the substrate with very high precision.
The materials used in the above type of photofabrication are typically photoresists. Photoresists can be used, for example, in the formation of bumps or metal posts by a plating process. Bumps or metal posts can be formed, for example, by forming a photoresist layer on top of a support, exposing the photoresist layer through a predetermined mask pattern, developing the layer to form a resist pattern in which the portions for forming the bumps or metal posts have been selectively removed (stripped), embedding a conductor such as copper into the stripped portions (the resist-free portions) using plating, and then removing the surrounding residual resist pattern.
As the photoresist, the patent references 1 through 3 listed below disclose the use of photopolymerizable photosensitive resin compositions, which are used for bump formation and wiring formation.
On the other hand, chemically amplified positive photoresists comprising an acid generator are known as photosensitive resin compositions with even better sensitivity than that provided by these photopolymerizable photosensitive resin compositions. The characteristic features of a chemically amplified photoresist are that on irradiation (exposure), acid is generated from the acid generator, generation of this acid is promoted by post exposure baking, and the base resin or the like of the resin composition then undergoes an acid-catalyzed reaction, thereby altering the alkali solubility of the reacted resin.
Chemically amplified photoresists include positive photoresists, in which irradiation causes alkali insoluble portions to become alkali soluble, and negative photoresists, in which irradiation causes alkali soluble portions to become alkali insoluble. Representative examples of chemically amplified negative resists include the resists comprising a combination of polyvinylphenol and a melamine derivative, as disclosed by James W. Thackeray et al. in the non-patent reference 1 listed below.
However, when a photoresist layer is produced using the chemically amplified resists mentioned above, the metal, such as aluminum or copper, used for the substrate or support, can inhibit the action of the acid on the resin within the resist layer, making it impossible to achieve the desired high precision resist pattern characteristics.
[Patent Reference 1]
Japanese Unexamined Patent Application, First Publication No. Hei 10-207057
[Patent Reference 2]
Japanese Unexamined Patent Application, First Publication No. 2000-39709
[Patent Reference 3]
Japanese Unexamined Patent Application, First Publication No. 2000-66386
[Non-patent Reference 1]
Proceedings of SPIE, volume 1086, pp. 34 to 47 (1989)